U.S. Pat. No. 4,439,746 to Epsztein discloses a microwave oscillator in which a wave guide cavity is provided with upstanding, apertured vanes and having coupling slots provided in the cavity between successive pairs of vanes.
U.S. Pat. No. 3,443,146 to Buck discloses a traveling wave tube wherein the delay structure discloses apertured propagating members extending from at least one wall of the tube, the propagating members being connected to one another at alternate positions by bars to form the equivalent of a helix slow wave structure.
U.S. Pat. No. 2,924,738 to Chodorow discloses a slow wave structure with interdigital apertured fins. The fins have alternating negative and positive potentials.
Many traveling wave tubes are known which include helically wound or coupled cavity slow wave structures.